I also don't think ssh keys are portable. When you reloaded your system the system generated new server keys. I can't say for sure though, and don't feel like looking it up. I'm lazy today.

Anyway, make sure your $HOME is chmod 700, and are you using a DSA key or an RSA key? DSA goes to authorized_keys2. I use DSA.

You need to delete your whole .ssh directory and start over. The private key needs to never leave the system it was generated on or it is considered compromised. The public key crosses the net, the private one is protected.

This isn't strictly required but IMO your .ssh directory should be chmod 700 too. Nobody else has any business poking around in there.

rm -rf .ssh
ssh-keygen -t dsa
scp .ssh/id_dsa.pub you@<remote-host-name-or-ip>:
ssh you@<remote-host-name-or-ip>
mkdir .ssh
mv id_dsa.pub .ssh/authorized_keys2
# You also want to delete your existing key for this host
exit
#now from your local machine again:
ssh you@<remote-host-name-or-ip>
# and you should be in without a password if you have a stock setup there.

Running a development version, I do re-installs fairly often, I do weekly backups of my home directory, when I do a new installation, I just restore the relevant directories back to /home/cariboo, in my case.